1. Technical Field
The present invention is directed to processes for fabricating devices, such as photodetector devices, in which two crystalline substrates with different crystal lattices are bound together.
2. Description of the Related Art
Processes for fabricating certain semiconductor devices require that two wafers, each having a crystal lattice that is different from the other, be bound together. For example crystalline III-V substrates (e.g. substrates of Indium Phosphide (InP) and Indium Gallium Arsenide (InGaAs)) substrates are bound to crystalline silicon substrates to fabricate photodetectors. Such devices are described in Hawkins, A., et al., "Silicon heterointerface photodetector," Appl. Phys. Lett., Vol. 68:26, pp. 3692-3694 (1996) (hereinafter Hawkins et al.). As used herein, III-V substrates are semiconductor compounds in which one of the elements is from column III of the Mendeleef Periodic Table and one of the elements is from column V of that Table.
Hawkins et al. describe a process for fabricating avalanche photodetector devices in which a silicon wafer is fused directly to an InGaAs surface of an indium phosphide (InP) substrate. In the Hawkins et al. process, an InGaAs surface is epitaxially grown on the InP substrate. The bonding surface of the silicon wafer is an epitaxial silicon layer grown on an n+ substrate with a shallow p-type implant at the surface. After bonding, the InP substrate is subsequently removed leaving only the InGaAs layer and the other thin device layers bound to the silicon substrate. The bonding is performed by pressing the surfaces of the two substrates together for 20 minutes at 650.degree. C. in an H.sub.2 atmosphere.
U.S. Pat. No. 5,207,864 describes low temperature fusion of dissimilar semiconductors. In the case in which both wafers are compound semiconductors, the wafers are lightly pressed together and left at a temperature at which one of the compositions can atomically rearrange at the interface. In the case in which one of the wafers is silicon, the wafers are pushed together in a strong acid. The wafers are adhered together with Van der Waals forces. Thereafter, they are pressed together and anealed at a temperature at which the non-silicon composition can atomically rearrange.
The quality of the semiconductor devices depends on, among other things, the quality of the silicon-InGaAs interface. Accordingly, a process for forming a high quality interface between the two different surfaces is desired.